1. Field of the Invention
This invention generally relates to electrical switches and electrical circuit breakers and, more particularly, to a combination device that is more convenient to operate and inexpensive to manufacture and to assemble.
2. Description of Related Art
It is well known to use a circuit breaker to protect one or more sensitive electrical components in electrical circuits from large currents such as may be caused by component malfunctions or external power surges. The circuit breaker, also known as a fuse, is connected between a power source and the components, or load, to be protected. The breaker contains an element, typically a bimetal, that "trips" when excessive current flows through it. The tripped element opens the circuit and disconnects the power source from the components, thereby preventing damage to the components.
Electrical equipment containing a circuit breaker commonly includes an on/off power switch electrically connected in series with the breaker for activation/deactivation of the equipment by a user. When the breaker trips due to a current overload, the user is supposed to perform the following three steps in sequence: first, turn the power switch off to its open position; second, reset the breaker; and then third, turn the power switch on to its closed position. If the overload current is still present, the breaker will trip again after the power switch is closed. If the overload current is no longer present, the equipment has been rendered operational again.
The art has proposed, in U.S. Pat. No. 4,528,538, to combine the power switch and the circuit breaker in a single device, and to render the combined device more convenient to operate after the breaker has been tripped by reducing the aforementioned three steps to two. Thus, the patented device provides an arrangement wherein opening the switch,after the breaker has been tripped, simultaneously resets the tripped breaker. Thereupon, closing the switch returns the device to normal operation.
Although generally satisfactory for its intended purpose, the device disclosed in the aforementioned patent has proven to be not altogether reliable in operation, complex in construction and relatively expensive to manufacture and assemble. The patented device has multiple parts and springs, all requiring precise placement. The patented device, in common with other circuit breakers, utilizes a synthetic plastic material gate plate which slides between and rubs against the breaker contacts. The plastic gate plate is thus exposed to electrical arcing at the breaker contacts. This arcing causes the plastic material of the gate plate to vaporize over time, and eventually the vaporized plastic coats the breaker contacts, as well as other exposed conductive surfaces within the device. The plastic coating is very disadvantageous and may interfere with the intended operation of the device. Electrical deterioration, including loss of accuracy of the bimetallic tripping element, are therefore inevitable consequences of such gate plate-type devices.
In addition, the patented device employs, for high amperage applications, silver contacts at the switch. However, the use of silver contacts is very expensive. Also, the tripping of the circuit breaker is not readily apparent to a user, particularly one located at a distance from the device. In addition, safety regulatory agencies require a circuit breaker to be "trip-free", i.e. the breaker must trip to the "off" position, even if a manually-operated switch/breaker actuator is deliberately held in an "on" position.